(1) Field of the Invention
The present invention relates to a novel racemic compound, a novel anti-ferroelectric liquid crystal composition containing the compound and a liquid crystal display device for which the composition is used.
(2) Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
A liquid crystal display device has been so far applied to a small-sized display device of various types due to its low-voltage operability, low-power consumption and display capability with a thin screen. Further, the liquid crystal display device is recently practically being applied to the fields of information and office automation-related machines and equipment and the field of television sets, and simultaneously, it is being applied to various fields of other use.
Under the circumstances, energetic developments are under way for attaining a large-sized liquid crystal display device of higher performance that has a higher display capacity and a higher display quality than a conventional CRT display device.
Liquid crystals used in currently available liquid crystal display devices are nematic liquid crystals, and they are classified into simple matrix driven liquid crystal devices and active matrix driven liquid crystal devices according to their driving methods.
Simple matrix driven liquid crystal display devices are produced advantageously in view of a cost due to their simple structures. However, these devices have the problems that the contrast is low due to a cross-talk phenomenon, that driving in a large capacity is difficult and that the display of video frames at a high duty ratio is difficult due to a low response speed. It is therefore necessary to break through many technical problems for attaining a large-sized liquid crystal display device capable of displaying video frames at a high duty ratio.
On the other hand, active matrix driven liquid crystal devices use a TFT (thin film transistor) method as a main stream, but it is required to form thin film transistors for each pixel, and a large investment is required for high production technology and the construction of a production line. The active matrix driving method is therefore far disadvantageous in view of a cost as compared with the simple matrix driving method. However, the active matrix driven liquid crystal device has a high contrast since the cross-talk phenomenon which is a problem of the simple matrix driving method is few, and further, its response speed is high. Therefore, there can be attained a liquid crystal display device which has a high image quality and is capable of displaying video frames at a high duty ratio. For this reason, the TFT method among the active matrix driving methods is gaining its position as a main stream.
At present, large-sized liquid crystal devices having a size of 10 to 20 inches are being developed, while the problem of viewing angle dependency, which is inherent to a device using the nematic liquid crystal, is critically serious. Various technical studies have been made for overcoming the viewing angle dependency, and as a result, displaying with a viewing angle of about 140.degree. has been possible without causing a gray scale inversion. However, the contrast is still dependent greatly upon a viewing angle, and at present, there cannot yet be obtained such flat contrast characteristics with regard to the wide viewing angle as achieved in CRT.
Under the above circumstances, a liquid crystal display device using a ferroelectric liquid crystal attracts attention as a fast response liquid crystal display device. A surface stabilized ferroelectric liquid crystal (SSFLC) device disclosed by Clark and Lagerwall attracts attention due to its high response speed and wide viewing angle which have not been available in the past. Its switching characteristics have been studied in detail, and a number of ferroelectric liquid crystal compounds have been synthesized for optimizing various physical property constants.
On the other hand, for accomplishing a practical device, there have been a number of technical barriers to be overcome such as difficulties in achieving a memory effect and controlling a layer structure due to the difficulty in controlling an alignment, the destruction of an alignment caused by a mechanical shock, and the like, and these problems have been overcome to produce a device as a product.
However, the ferroelectric liquid crystal display device still has problems that it cannot display colors since it cannot handle, in principle, a gray scale and that the display of video frames is difficult because high speed response has not been attained yet.
Further, as another high speed response liquid crystal display device, the development of a device having a switching mechanism different from that of SSFLC is also under way. This is a liquid crystal display device which utilizes switching among tri-stable states of a liquid crystal having an anti-ferroelectric phase (to be referred to as "anti-ferroelectric liquid crystal" hereinafter) (Japanese Journal of Applied Physics, Vol. 27, pp. L729, (1988)).
The anti-ferroelectric liquid crystal has the following three stable states.
That is, the above three stable states are two uniform states (Ur, Ul) observed in two ferroelectric crystal states and one third state. Chandani et al report that the above third state is an anti-ferroelectric phase (Japanese Journal of Applied Physics, vol. 28, pp. L1261 (1989) and Japanese Journal of Applied Physics, vol. 28, pp. L1265 (1989)).
The above switching among the tri-stable states is the first characteristic of an anti-ferroelectric liquid crystal.
The second characteristic of the anti-ferroelectric liquid crystal is that a sharp threshold is present with regard to an applied voltage.
Further, it has a memory effect when a proper bias voltage is set, which is the third characteristic of the anti-ferroelectric liquid crystal.
Further, the fourth characteristic of the anti-ferroelectric liquid crystal is that its layer structure can be easily switched when an electric field is applied (Japanese Journal of Applied Physics, Vol. 28, pp. L119, (1989), and vol. 29, pp. L111 (1990)). Owing to this characteristic, a liquid crystal display device almost free of defects and having self-restoring ability of the alignment can be produced.
By utilizing those characteristics described above, a liquid crystal device having a high response speed and an excellent contrast can be achieved.
Further, it has been demonstrated that the gray shade display, which is almost impossible to achieve with a ferroelectric liquid crystal device, is possible to achieve with an anti-ferroelectric liquid crystal device. It has been consequently made possible to shift toward a full-color display, and the importance of an anti-ferroelectric liquid crystal is further increasing (Preprints of No. 4 Ferroelectric Liquid Crystal International Symposium, page 77, (1993)).